extract data from one Matrix into three matices

I have created meshgrid [x,y] on which i have to contourf z.

But the problem is that i have 3 different types of data in z;

1- -999 (which shows no-data) 2- -9999 (which shows invalid-data) 3- valid data on which I would like to plot the actual contour.

I am trying to show all three types of data in z on the contour.

My strategy is to separate z into three matrices each containing one particular type of data among three mentioned types, keeping the size of all three matrices same as original z, so that i can contour all the three new matrices on same [x,y] grid.

Any Idea how to separate z into three matrices of same size as original ("No values" in the matrix can be treated as no vales)? I can use find(z=-999) to get the index of data type 1 in z but don't know how can i get the matrix from that index.

Best regards